The present invention relates to improvements in the method for forming an image by color reaction between a ligh-receiving sheet and an image-receiving sheet. A photo-sensitive and pressure-sensitive image forming member made up of a light-receiving sheet coated with a layer of microcapsules including a photopolymerization agent and colorless dye through a binder resin and an image-receiving sheet coated with a layer of a developer material for coloring the colorless dye through a binder resin is already disclosed in U.S. Pat. No. 4,399,209. The method for image formation using such a photo-sensitive and pressure-sensitive image forming member will be briefly described below. When the aforesaid light-receiving sheet is selectively illuminated by image forming light, such as reflected light from an original, the photopolymerization agent in the microcapsules located at the position exposed to the light is cured by polymerization and a cured image is thereby formed. Then the light-receiving sheet and the image-receiving sheet are laid one upon the other and pressed together by means of pressure rollers or the like, whereby the microcapsules which are not cured by polymerization are ruptured and the colorless dye contained therein flows out to attach to the image-receiving sheet and forms a color image by reaction with the a developer material on the image receiving sheet. A colored image is thus formed on the image-receiving sheet.
In the above described image forming method, however, extremely high pressure is required for causing the light-receiving sheet and the image-receiving sheet sandwiched one upon the other to be compressed so that the microcapsules may be ruptured. Hence, sometimes there are formed wrinkles in the light-receiving sheet and image-receiving sheet.
Further, when forming an image according to the described method, it sometimes occurs that the color is not formed sufficiently because of a slow reaction rate between the colorless dye and the developer material and hence the formed image becomes blurred. Therefore, it has been practiced to heat the image-receiving sheet with the colored image formed thereon through the compression by the pressure rollers by means of a heat roller or the like so that the coloring reaction may be promoted. However, when a heat roller is used and its surface temperature is raised several ten degrees above 100 degrees to accelerate the reaction rate, it sometimes occurs that the binder of the image-receiving sheet attaches to the heat roller and offsetting is caused.